I'm undecided as to whether these are the right colors for this guy. I think he might actually sit well as a four-color cars, if I added blue.
I"m also torn as to whether I should give him an activated ability. It would remove a bit of the challenge of making a combine piece out of him.

Heee. What would this do? Let's see... Sadly it wouldn't work with Alexi, Zephyr Mage or her cycle, nor Atogatog/Bosh, Iron Golem/etc. There are lots of legends with fairly cheap activated abilities that don't benefit from this.

Other bad combos: Boris Devilboon starts doing a Sprout Swarm impression. Borborygmos Enraged turns all your creatures into better-than-pingers. Cromat's abilities at least become less fiddly to activate. Horde of Notions can cast things a heck of a lot more cheaply - especially Nameless Inversion or Consuming Bonfire - and similarly Mayael the Anima. Jaya Ballard, Task Mage decides spellshaping is for wimps and starts torching things with more gusto. You can move around the Shield and Sword of Kaldra without paying as much mana! Ulasht, the Hate Seed can make tokens or deal damage... still rather less efficiently than other things in this list.

Some actually-good combos: ­Ib Halfheart, Goblin Tactician spews Goblins onto the battlefield at an impressive rate every turn; Rhys the Redeemed even more so. That's a heckuva lot of tokens. ­Helvault / Legacy Weapon / Tetsuo Umezawa get rather cheaper to activate, though still not much better that Visara the Dreadful with this out (and she's much better if you don't find this). Shattergang Brothers similarly fire off targeted Edicts a lot more freely. Kamahl, Fist of Krosa casts Overrun every turn, though he does need to tap a couple of your tokens (or lands) to do so. Uyo, Silent Prophet gives all your spells Conspire, or rather multi-Conspire.

The really terrifying combos: The Grandeur cycle work well with this. Baru, Fist of Krosa splurges giant Elementals onto the board (as does Dokai, Weaver of Life); Tarox Bladewing can easily hit 16/15, 32/31, or higher; and Oriss, Samite Guardian gives an instant Isochron Scepter-Orim's Chant lock.

The other cycle that works really well is the Myojin. Myojin of Cleansing Fire will kill Voradin, like Mageta the Lion; but Myojin of Life's Web, Myojin of Night's Reach, and Myojin of Seeing Winds are all pretty absurd effects to cast every turn (especially if you're chaining Seeing Winds, or equivalently Griselbrand, into Life's Web).

All in all, this would make for a hilarious commander for a Captain Sisay-themed deck :)

I'm so excited to see you listing out all of these potential combos. I knew there would be quite a few, but it's very interesting to see someone else come up with them.
You've listed mainly activated abilities, but I believe I worded this so that it can play with triggered abilities, as well. Intet, the Dreamer and her dragon friends would like this. So would Lorthos, the Tidemaker.